The control system of the present invention could be applied to any hydraulically actuated system that reacts to a load. For example, the control system could be applied to hydraulically actuated press brakes, hydraulically actuated off-road equipment and the like. For purposes of an exemplary showing, the invention will be described in its application to a conventional hydraulically operated, C-frame, metal working press. An example of such a press is taught in U.S. Pat. No. 4,242,901.
In the development of this general class of presses, most of the earliest presses were mechanically actuated. The mechanical presses were characterized by a high number of strokes or work cycles per unit of time, but tonnage was achieved only at the bottom of the stroke and the work stroke was capable of minimal adjustments.
Prior art workers then turned their attention to hydraulically actuated presses which overcame most of the disadvantages of the mechanical presses, and offered additional advantages made possible through the use of hydraulic systems. However, hydraulically actuated presses were characterized by relatively slow cycle times.
Today, many industries are working with small production quantities. Under these circumstances, there is a need for a general purpose press capable of high production rates. The present invention is based upon the discovery that if a conventional hydraulic C-frame metal working press is provided with a control system utilizing cartridge valves in the hydraulic system actuated by a programmable signal processor, all of the advantages of hydraulic systems can be retained and improved upon, while achieving cycle speeds heretofore obtainable only with mechanically actuated presses.
The control system of the present invention permits close control of the movement of the press slide with various speed options available for approach to the workpiece, pressing of the workpiece and retraction of the slide. The position of the ram or slide is always known and the up-stroke of the ram can be initiated on the basis of tonnage or position. Further, the control system of the present invention optimizes decompression of hydraulic pressure in an adaptive manner, based upon the particular load conditions being encountered. This not only prevents hydraulic fluid surges, noise, and damage to the equipment, but also increases production speed capability, and allows the hydraulic fluid cooler and filter to be located in the main hydraulic circuit.